[PATCH v2 3/3] sparc64: Randomize the load address of PIE executables

[Stian Halseth <stian@itx.no>]

On sparc64 every PIE executable (ET_DYN with PT_INTERP) is loaded at
exactly ELF_ET_DYN_BASE, with its brk heap at a fixed offset after it.
The stack and the mmap base are randomized; the program image and brk
are not.

load_elf_binary() adds arch_mmap_rnd() to the load bias and calls
arch_randomize_brk(), but without ARCH_HAS_ELF_RANDOMIZE both are
no-ops. sparc64 already has a suitable mmap_rnd() for the mmap base.
Rename it to arch_mmap_rnd(), add arch_randomize_brk() with the ranges
x86 and the generic version use, and select ARCH_HAS_ELF_RANDOMIZE.

Closes: https://github.com/sparclinux/issues/issues/119
Tested-by: Jan Engelhardt <jengelh@inai.de>
Signed-off-by: Stian Halseth <stian@itx.no>
---
 .../features/vm/ELF-ASLR/arch-support.txt          |  2 +-
 arch/sparc/Kconfig                                 |  1 +
 arch/sparc/kernel/sys_sparc_64.c                   | 14 ++++++++++++--
 3 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/Documentation/features/vm/ELF-ASLR/arch-support.txt b/Documentation/features/vm/ELF-ASLR/arch-support.txt
index 57406c0d53531..d4a34c9fbae86 100644
--- a/Documentation/features/vm/ELF-ASLR/arch-support.txt
+++ b/Documentation/features/vm/ELF-ASLR/arch-support.txt
@@ -24,7 +24,7 @@
     |       riscv: |  ok  |
     |        s390: |  ok  |
     |          sh: | TODO |
-    |       sparc: | TODO |
+    |       sparc: |  ok  |
     |          um: | TODO |
     |         x86: |  ok  |
     |      xtensa: | TODO |
diff --git a/arch/sparc/Kconfig b/arch/sparc/Kconfig
index ab77d3f2536e1..82c989b9e7831 100644
--- a/arch/sparc/Kconfig
+++ b/arch/sparc/Kconfig
@@ -71,6 +71,7 @@ config SPARC64
 	def_bool 64BIT
 	select ALTERNATE_USER_ADDRESS_SPACE
 	select ARCH_HAS_DELAY_TIMER
+	select ARCH_HAS_ELF_RANDOMIZE
 	select HAVE_FUNCTION_TRACER
 	select HAVE_FUNCTION_GRAPH_TRACER
 	select HAVE_KRETPROBES
diff --git a/arch/sparc/kernel/sys_sparc_64.c b/arch/sparc/kernel/sys_sparc_64.c
index 087595fa43081..2948d5769e768 100644
--- a/arch/sparc/kernel/sys_sparc_64.c
+++ b/arch/sparc/kernel/sys_sparc_64.c
@@ -26,6 +26,8 @@
 #include <linux/ipc.h>
 #include <linux/personality.h>
 #include <linux/random.h>
+#include <linux/elf-randomize.h>
+#include <linux/sizes.h>
 #include <linux/export.h>
 #include <linux/context_tracking.h>
 #include <linux/timex.h>
@@ -280,7 +282,7 @@ unsigned long get_fb_unmapped_area(struct file *filp, unsigned long orig_addr, u
 EXPORT_SYMBOL(get_fb_unmapped_area);
 
 /* Essentially the same as PowerPC.  */
-static unsigned long mmap_rnd(void)
+unsigned long arch_mmap_rnd(void)
 {
 	unsigned long rnd = 0UL;
 
@@ -294,9 +296,17 @@ static unsigned long mmap_rnd(void)
 	return rnd << PAGE_SHIFT;
 }
 
+unsigned long arch_randomize_brk(struct mm_struct *mm)
+{
+	if (test_thread_flag(TIF_32BIT))
+		return randomize_page(mm->brk, SZ_32M);
+
+	return randomize_page(mm->brk, SZ_1G);
+}
+
 void arch_pick_mmap_layout(struct mm_struct *mm, const struct rlimit *rlim_stack)
 {
-	unsigned long random_factor = mmap_rnd();
+	unsigned long random_factor = arch_mmap_rnd();
 	unsigned long gap;
 
 	/*
-- 
2.43.0